CO-PENDING PATENT APPLICATIONS
This application is related to the following:
1) copending U.S. application Ser. No. 08/872,817, entitled, A GAS SENSOR WITH MULTIPLE EXPOSED ACTIVE ELEMENTS, attorney docket no. CTS-1508, filed Jun. 11, 1997, PA1 2) copending U.S. application Ser. No. 08/872,987, entitled A GAS SENSOR WITH MULTI-LEVEL INSENSITIVITY CIRCUITRY, attorney docket no. CTS-1518, filed Jun. 11, 1997, and PA1 3) copending U.S. application Ser. No. 60/017,112, entitled, FUEL SYSTEM LOW CURRENT RHEOSTAT, attorney docket no. CTS-1491, filed May 9, 1996.
The aforementioned are assigned to the assignee named in the present application and are herein incorporated by reference in their entirety.
1. Field of the Invention
This invention relates to a gas sensor, and specifically to a sensor that can rotate about an axis without having a reference sensor element exposed to excess heat generated by a proximate catalyzed sensor element.
2. Description of the Related Art
Various devices are well known for combustible gas detectors used to detect the presence of combustible gases such as those found in car engines. Typical circuits are configured to include at least one sensing element that may be a wire having a catalytic coating. The sensing element was used as one of four legs of a wheatstone bridge circuit. The other three legs consisted of two resistors and a compensator element. The compensator element was identical to the sensing element except that it did not bear a catalytic coating.
A current or voltage was applied to the bridge circuit to heat the surface of the catalytic coating affixed to the sensing element. Since the resistance values of the other three legs of the bridge were known, the resistance in the sensing element could be determined as the current or voltage was passed through the bridge.
When the sensing element was exposed to a combustible gas, such as hydrocarbon, the catalytic coating would begin to burn, increasing the temperature of the sensing element. As the temperature of the sensing element increased, the resistance of the element increased. Accordingly, the current passing through the element decreased. By comparing the resistance level of the sensing element to the resistance level of the compensator element, the presence of a combustible gas could detected. Since the amount of gas present caused a nearly linear increase or decrease in the resistance of the sensing element, the quantity of the gas could be accurately determined by calibrating the change in resistance. This is the basic principal of operation of a catalytic combustible gas sensor. It is noted that often the sensing element must be at a predetermined elevated temperature to properly cause the catalyst reaction with the designated gas.
3. Related Art
Examples of patents related to the present invention are as follows, and each patent is herein incorporated by reference for the supporting teachings:
U.S. patent statutory registration no. H454, is a chemical agent leak detector and a method of using the same.
U.S. Pat. No. 5,400,643, is a gas sensor based on semiconductor oxide, for gaseous hydrocarbon determination.
U.S. Pat. No. 5,388,443, is an atmosphere sensor and method for manufacturing the sensor.
U.S. Pat. No. 5,365,216, is a catalyst monitoring device using EGO sensors.
U.S. Pat. No. 5,363,091, is a catalyst monitoring device using EGO sensors.
U.S. Pat. No. 5,211,053, is a hot gas sensor device with improved thermal isolation from carrier plate.
U.S. Pat. No. 5,012,671, is a gas detecting device.
U.S. Pat. No. 4,991,424, is an integrated circuit heatable sensor.
U.S. Pat. No. 4,984,446, is a gas detecting device and gas detecting system using the same.
U.S. Pat. No. 4,928,513, is a sensor.
U.S. Pat. No. 4,839,767, is an element and device for detecting internal faults in an insulating gas charged electrical apparatus.
U.S. Pat. No. 4,816,800, is an exhaust gas sensor.
U.S. Pat. No. 4,674,319, is an integrated circuit sensor.
U.S. Pat. No. 4,377,944, is an integrated gas sensitive unit comprising a gas sensitive semiconductor element and a resistor for gas concentration measurement.
U.S. Pat. No. 3,901,067, is a semiconductor gas detector.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants' acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, applicant's claimed invention.
4. A Related Problem
Referring to FIG. 1, there is a previous design from the present inventors that illustrates one problem to be overcome by the additionally now disclosed preferred embodiments. Specifically, there is a sensor 10 having a base 12 with signal conditioning circuitry 14 that receives signals via traces 24 and 26 from sensing element structures 17 and 19, which are located on either side of longitudinal axis 11. Uniquely, the sensing element structures 17 and 19 are made up of sensing elements 20 and 21 that are located on parallel bridges 22 and thermally isolated by voids 18. In operation, one skilled in the art will realize that all of the electrical signals will be skewed if the heated air flow 27 first interacts with the catalyzed sensing element and then contacts the reference sensor. The air contacting the reference sensor will have been heated by the catalytic reaction, thus skewing any resulting signals. To avoid this problem, great care must be given to ensure that the air 27 does not contact the sensor elements in this fashion. In particular, the sensor would have to be placed so the air either hits both sensors simultaneously or hits the reference sensor first. In either case it is very difficult to make sure that the sensor is so arranged when placing it in an exhaust gas air stream. However, the present invention has overcome the need for careful placement of the sensor 10 in air stream 27 and thus eliminating the potential signal skewing problem.
This and other problems will be solved by the preferred embodiments of the invention. A review of the specification, drawings, and claims will more clearly teach a skilled artisan of other problems that are solved by the preferred embodiments.